A film metal clad laminate, in which a metal layer (a foundation metal layer/an upper metal electric conductive layer) is formed on a polyimide resin film with excellent heat resistance, has been used for flexible circuit boards. The foundation metal layer is formed of nickel, etc., and the upper metal electric conductive layer is formed of Cu, etc. The film has high water absorption, and dimensional stability thereof worsens under humid atmosphere. Accordingly, as a replacement of the film, a liquid crystal polyester film with excellent heat resistance and low water absorption is focused.
The liquid crystal polyester film is said to have poor adhesion with a metal layer (for example, Ni layer/Cu layer). Therefore, Patent Reference 1 has proposed a method for manufacturing a metal clad laminate for improving adhesion between the film and the metal layer through a heat treatment.
Patent Reference 2 has proposed a method for manufacturing a metal clad laminate for improving an adherence strength between a liquid crystal polyester film and a electrically conductive metal film, in which a surface of the liquid crystal polyester film is roughened with an etching liquid, and then the metal clad laminate is heated at a predetermined temperature within a range from 100° C. to a temperature near a liquid crystal transition point temperature after an electrically conductive metal film is formed on the roughened surface of the film with a plating method.    Patent Reference 1: Japanese Patent Publication No. 3693609    Patent Reference 2: Japanese Patent Publication No. 2004-307980
The liquid crystal polyester film has crystal orientation in a planar direction thereof. Accordingly, the film itself tends to slightly expand in the planar direction thereof after the heat treatment. Therefore, in the above method, when a nickel alloy is plated on the film as a base foundation layer, a dimensional of the metal clad laminate becomes large when a circuit is formed through conductor etching. That is, the metal clad laminate has poor dimensional stability, and is not suitable for forming a fine circuit. Moreover, the adherence strength between the liquid crystal polyester film and the electrically conductive metal layer is not practically sufficient.
An object of the present invention is to solve the above problems, and to provide a method for manufacturing a metal clad laminate capable of improving adhesion of a flexible thermoplastic polymer film with a metal layer and dimensional stability during the conductor etching.